#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <set>
#include <bitset>
#include <utility>
using namespace std;

#define mm(a, n) memset(a, n, sizeof a)
#define mk(a, b) make_pair(a, b)

const double eps = 1e-6;
const int INF = 0x3f3f3f3f;

typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef pair<int, LL> PIL;

inline void quickread() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
}

vector<int> res;
unordered_map<int, int> mp;
int n;
// 模拟
inline void solution() {
    cin >> n;
    for (int i = 0; i < n; i ++ ) {
        int val;
        cin >> val;
        if (!mp.count(val)) 
            res.push_back(val), mp[val] ++ ;
        else
            mp[val] ++ ;
    }
    for (auto & x : res) {
        if (mp[x] == 1) {
            cout << x << endl;
            return ;
        }
    }
    cout << "None" << endl;
}

int main() {
    freopen("input.txt", "r", stdin);
    quickread();
    solution();
    return 0;
}